Litter and its impact on our environment is receiving increased national attention. In response to this problem, some states have enacted legislation which has banned the use of throw-away plastic, glass, and metal beverage bottles. Recent studies have shown that this legislation has reduced the amount of litter on our highways and other public property. However, this legislation has also created other unforeseen problems in the storage and return of returnable beverage bottles.
It is common practice in the beverage industry to use plastic receptacles for shipping glass, plastic and metal beverage containers. These plastic receptacles are normally formed with a plurality of stiffening flanges and ribs which form a large number of crevices within which dirt can accumulate. In some instances, the plastic receptacles are composite structures which include removable secondary enclosures. For hygenic and aesthetic purposes, it is desirable to clean these receptacles each time they are returned to the bottling plant.
The art of cleaning an object by dipping it in an acidic or basic cleaning solution so that the chemical solution attacks the surface contaminants is well known. This method is economical and requires only the most simple equipment. However, it is also time consuming and does not always clean the crevices and holes in the object being so processed. Furthermore, the cleaning solution often attacks the surface of the object itself and, after a substantial number of cleaning cycles, may have a permanent detrimental effect on the appearance of the surface.
Cleaning objects by placing them in a liquid bath and transmitting ultrasonic waves through the fluid in the bath to impinge upon the surface of the object is also well known. An example of a cleaning apparatus using ultrasonic waves is disclosed in the parent application to the present case. The ultrasonic cleaning method is more effective at removing dirt than merely immersing the object in a chemical bath. Unfortunately, as the length of time that any one object is immersed in the bath is decreased, the number of transducers needed to properly clean the object is increased to make ultrasonics effective, there must be at least one transducer element per gallon of cleaning fluid. While batch cleaning using ultrasonics is well known, it is sometimes extremely expensive to use ultrasonic cleaning equipment to adequately clean objects in a very high volume production line situation. Furthermore, ultrasonic transducers only loosen the dirt but do not remove the dirt unless there is sufficient exposure time and a sufficient amount of ultrasonic energy. A thorough rinse is therefore essential to remove the dirt from the object. Finally, all ultrasonic cleaners have the disadvantage of being incapable of removing large pieces of debris from the crevices and cavities of the subject being cleaned. Such pieces of debris as straw, broken glass and bottle caps are often found within the plastic receptacles used by the beverage industry when they are returned to the bottling plant.
One method that has been used to increase the effectiveness of ultrasonic cleaning devices is to provide a pre-wash station where the object is scrubbed prior to being immersed in the ultrasonic immersion bath. In the pre-wash station, the object may, for example, be exposed to the scrubbing action of a high pressure spray of cleaning fluid. One disadvantage with the use of a pre-wash station is that the cleaning fluid from the pre-wash station cannot be permitted to flow into the immersion chamber. If the cleaning fluid from the pre-wash station is allowed to flow into the immersion chamber and to mix with the cleaning fluid therein, the effectiveness of the ultrasonic transducers will be greatly decreased.
In the parent application to the present application, it was proposed that a cleaning apparatus be provided with a liquid immersion bath combining a chemical and a mechanical cleaning action. The chemical cleaning action was provided by using a cleaning fluid which reduces the surface tension of the dirty object and of the dirt itself. The mechanical cleaning action was provided by either transducers or a series of high pressure spray jets which agitated the fluid in the bath. While this apparatus produced the desirable result of decreasing the number of transducers needed for a predetermined amount of dirt removal, the apparatus still required the use of more caustic chemicals in the cleaning fluid than may be desirable. Furthermore, the specific apparatus disclosed did not suggest that the fluid from the pre-wash station could be permitted to be mixed with the fluid in the immersion bath.